Such switches are used for electric tools, for example for handheld electric tools, such as electric drills, hammer drills, electric screwdrivers or the like.
The electrical energy from the power supply system or a suitable rechargeable battery system is converted or influenced with the aid of the electrical switch in such a way that an electric motor for the electric tool, said electric motor being arranged downstream of the switch, is driven as determined by the operator. Thus, for example, the electric motor is switched on and/or off, braked, its speed is changed or else it is regulated in a torque-dependent and/or current-dependent fashion.
DE 197 08 939 A1 has disclosed an electrical switch which is suitable for these functions with an actuating mechanism which can be adjusted manually between an initial position and a final position. If the actuating mechanism is moved out of the initial position, a contact system of the switch is switched on so as to bring an electric motor of the electric tool into operation. Furthermore, the actuating mechanism is operatively connected to a potentiometer, which emits an electrical voltage corresponding to the adjustment path of the actuating mechanism. The potentiometer therefore acts as a signaling device for generating a signal associated with the adjustment path of the actuating mechanism, with this signal in this case being represented by the electrical voltage, whose magnitude corresponds to the adjustment path of the actuating mechanism. This signal is supplied to a control device in the switch, the control device operating the electric motor or subjecting said electric motor to open-loop and/or closed-loop control depending on this signal. For example, the control device sets the speed of the electric tool corresponding to the adjustment of the actuating mechanism performed by the user. If the actuating mechanism enters the final position, a contact system which serves to bridge the control device is switched on, whereupon the electric motor is operated on the full voltage. The actuating mechanism therefore has a switching effect on the respective contact system in each position, namely when it leaves the initial position and when it reaches the final position.
It has been shown with the known switch that the contact system can fail prematurely. In particular, in switches using open-loop or closed-loop control electronics when using electric tools which are subject to severe stress, the contact system, to be precise primarily that for the bridging contact, can be caused to fail. This negative effect, the so-called teasing of the contact system, primarily occurs in low-voltage applications in the AC voltage and DC voltage sector. Furthermore, teasing is also established when the electric tool is operated under vibrations, i.e. in the percussion drilling mode or in the hammer drilling mode, for example.